Optical waveguide feedthrough assembly

ABSTRACT

An optical waveguide feedthrough assembly passes at least one optical waveguide through a bulk head, a sensor wall, or other feedthrough member. The optical waveguide feedthrough assembly comprises a cane-based optical waveguide that forms a glass plug sealingly disposed in a feedthrough housing. For some embodiments, the optical waveguide includes a tapered surface biased against a seal seat formed in the housing. The feedthrough assembly can include an annular gold gasket member disposed between the tapered surface and the seal seat. The feedthrough assembly can further include a backup seal. The backup seal comprises an elastomeric annular member disposed between the glass plug and the housing. The backup seal may be energized by a fluid pressure in the housing. The feedthrough assembly is operable in high temperature and high pressure environments.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/172,616, filed Feb. 25, 2011 and entitled “Optical WaveguideFeedthrough Assembly,” which is related to U.S. application Ser. No.11/172,617, now issued U.S. Pat. No. 7,447,390, filed Jun. 30, 2005 andentitled “Pressure Transducer with Optical Waveguide FeedthroughAssembly,” both of which are herein incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to feedthroughs for optical waveguides,and more particularly, to hermetically sealed feedthroughs suitable foruse in high pressure, high temperature, and/or other harsh environments.

2. Description of the Related Art

In many industries and applications, there is a need to have smalldiameter wires or optical waveguides penetrate a wall, bulkhead, orother feedthrough member wherein a relatively high fluid or gasdifferential pressure exists across the feedthrough member. In addition,one or both sides of the feedthrough member may be subjected torelatively high temperatures and other harsh environmental conditions,such as corrosive or volatile gas, fluids and other materials.

In the case of electrical systems, these devices, called feedthroughs orpenetrators, typically are constructed by using metal ‘pins’ exhibitinghigh conductivity and a low thermal coefficient of expansion. The pinsare concentrically located within a hole in a housing, and the resultingannular space is filled with a suitable sealing glass or other material.Critical to the success of such seals is the selection of the metalhousing, sealing glass, and electrical pin to ensure completion of acompression seal around the ductile inclusion (pin). As the operatingtemperature range of the feedthrough increases, the control of thermalexpansion rates becomes increasingly important in order to avoid failureof the feedthrough by excessive thermal stress at the interface layersbetween the various materials. This technology is relatively mature forelectrical feedthroughs, and commercial devices are readily availablethat meet service temperatures in excess of 200° C.

More recently, with the introduction of optical sensors, particularlysensors for use in oil and gas exploration and production and for lifein harsh industrial environments, a need has emerged for a bulkheadfeedthrough that can seal an optical fiber at high pressures of 20,000psi and above, and high temperatures of 150° C. to 300° C., with aservice life of 5 to 20 years. An exemplary sensing assembly for use inharsh environments is disclosed in U.S. Pat. No. 6,439,055, which issuedon Aug. 27, 2002, entitled “Pressure Sensor Assembly Structure ToInsulate A Pressure Sensing Device From Harsh Environments”, which isassigned to the Assignee of the present application and is incorporatedherein by reference in its entirety.

There are several problems associated with constructing such an opticalfiber feedthrough. One of these problems is the susceptibility of theglass fiber to damage and breakage. This is due to the flexibility ofthe small size fiber, the brittle nature of the glass material, and thetypical presence of a significant stress concentration at the pointwhere the fiber enters and exits the feedthrough. Attempts to use asealing glass, such as that used with electrical feedthroughs, have hadproblems of this nature due to the high stress concentration at thefiber-to-sealing glass interface.

Another problem with sealing an optical fiber, as opposed to sealing aconductive metal “pin” in an electrical feedthrough, is that the fusedsilica material of which the optical fiber is made, has an extremely lowthermal expansion rate. Compared to most engineering materials,including metals, sealing glasses, as well as the metal pins typicallyused in electrical feedthroughs, the coefficient of thermal expansion ofthe optical fiber is essentially zero. This greatly increases thethermal stress problem at the glass-to-sealing material interface.

One technique used to produce optical fiber feedthroughs is the use of asealed window with an input and an output lensing system. In thistechnique, the optical fiber must be terminated on each side of apressure-sealed window, thus allowing the light to pass from the fiberinto a lens, through the window, into another lens, and finally into thesecond fiber. The disadvantages associated with this system include thenon-continuous fiber path, the need to provide two fiber terminationswith mode matching optics, thus increasing manufacturing complexity andincreasing the light attenuation associated with these features.

It is often desirable to mount fiber optic based sensors in harshenvironments that are environmentally separated from other environmentsby physical bulkheads. An exemplary such fiber optic based sensor isdisclosed in co-pending U.S. patent application Ser. No. 09/205,944,entitled “Tube-Encased Fiber Grating Pressure Sensor” to T. J. Bailey etal., which is assigned to the Assignee of the present invention and isincorporated herein by reference in its entirety. This exemplary opticalsensor is encased within a tube and certain embodiments are disclosedwherein the sensor is suspended within a fluid. The sensor may be usedin a harsh environment, such as where the sensor is subjected tosubstantial levels of pressure, temperature, shock and/or vibration. Incertain environments, such sensors are subjected to continuoustemperatures in the range of 150° C. to 250° C., shock levels in excessof 100Gs, and vibration levels of 5G RMS at typical frequencies betweenabout 10 Hz and 2000 Hz and pressures of about 15 kpsi or higher.

However, as discussed above, the harsh environments where the sensorsare located generally must be isolated by sealed physical barriers fromother proximate environments through which the optical fibercommunication link of the sensor must pass. It is important to seal thebulkhead around the optical fiber to prevent adjacent environments inthe sensor from contaminating the optical fiber communication link. Ifthe optical communication fiber is compromised by contamination from anadjacent harsh sensor environment, the optical fiber and all sensors towhich it is connected are likely to become ineffective.

There is a need therefore, for an optical waveguide feedthrough assemblycapable of operating in relative high temperature and high pressureenvironments.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide an optical waveguidefeedthrough assembly, and a method of making such an assembly, whichovercomes one or more of the above-described drawbacks and disadvantagesof the prior art, and is capable of relatively long-lasting operation atrelatively high pressures and/or temperatures.

An optical waveguide feedthrough assembly passes at least one opticalwaveguide through a bulk head, a sensor wall, or other feedthroughmember. The optical waveguide feedthrough assembly comprises acane-based optical waveguide that forms a glass plug sealingly disposedin a feedthrough housing. For some embodiments, the optical waveguideincludes a tapered surface biased against a seal seat formed in thehousing. The feedthrough assembly can include an annular gold gasketmember disposed between the conical glass surface and the metal sealseat. The feedthrough assembly can further include a backup seal. Thebackup seal comprises an elastomeric annular member disposed between theglass plug and the housing. The backup seal may be energized by a fluidpressure in the housing. The feedthrough assembly is operable in hightemperature and high pressure environments.

The conical taper of the glass waveguide surface is designed to becomplementary to the bulkhead seal seat. The role of the gold gasket isto accommodate practical manufacturing tolerances on the surfacefinishes of the glass plug and the bulkhead seal seat. Furthermore, therole of the backup elastomeric seal is to accommodate practicalmanufacturing tolerances on the shape functions the glass plug and thebulkhead seal seat.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 illustrates a cross section view of an optical waveguidefeedthrough assembly.

FIG. 2 illustrates a cross section view of an optical waveguidefeedthrough assembly having diagnostic sensors disposed therein.

FIGS. 3-5 illustrate graphs of signals received from the diagnosticsensors where the feedthrough assembly is at a fixed temperature anddifferent pressure for each graph.

FIGS. 6-8 illustrate graphs of signals received from the diagnosticsensors where the feedthrough assembly is at a fixed pressure anddifferent temperature for each graph.

FIG. 9 illustrates a cross section view of an optical waveguidefeedthrough assembly that provides bi-directional seal performance.

FIG. 10 illustrates a cross sectional view of an optical waveguidefeedthrough assembly that includes a compression seal element.

FIG. 11 illustrates the optical waveguide feedthrough assembly shown inFIG. 10 after compression of the compression seal element.

FIG. 12 illustrates a cross section view of another optical waveguidefeedthrough assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Epoxy-free optical fiber feedthrough assemblies applicable for use inhigh temperature, high pressure environments are provided. In oneembodiment, a feedthrough assembly includes a glass plug disposed in arecess of a feedthrough housing. The glass plug is preferably alarge-diameter, cane-based, waveguide adapted to seal the recess in thehousing and provide optical communication through the housing. Allembodiments described herein provide for sealing with respect to thehousing at or around the glass plug of an optical waveguide elementpassing through the housing.

As used herein, “optical fiber,” “glass plug” and the more general term“optical waveguide” refer to any of a number of different devices thatare currently known or later become known for transmitting opticalsignals along a desired pathway. For example, each of these terms canrefer to single mode, multi-mode, birefringent, polarizationmaintaining, polarizing, multi-core or multi-cladding opticalwaveguides, or flat or planar waveguides. The optical waveguides may bemade of any glass, e.g., silica, phosphate glass, or other glasses, ormade of glass and plastic, or solely plastic. For high temperatureapplications, optical waveguides made of a glass material is desirable.Furthermore, any of the optical waveguides can be partially orcompletely coated with a gettering agent and/or a blocking agent (suchas gold) to provide a hydrogen barrier that protects the waveguide. Inaddition, the feedthrough assemblies can include a single such opticalwaveguide or may include a plurality of such optical waveguides.

AN EXEMPLARY FEEDTHROUGH ASSEMBLY

FIG. 1 shows a cross section view of an optical fiber feedthroughassembly 100 that includes a front housing 10 coupled to a back housing12. An optical waveguide element 14 passes through a passageway 16common to both housings 10, 12. The passageway 16 is defined by boresextending across the housings 10, 12. The optical waveguide element 14includes a glass plug 18 defining a large-diameter, cane-based, opticalwaveguide preferably having an outer diameter of about 3 millimeters(mm) or greater. The glass plug 18 can have appropriate core andcladding dimensions and ratios to provide the desired outerlarge-diameter.

For some embodiments, first and second fiber pigtails 19, 20 extend fromeach end of the glass plug 18. Each of the pigtails 19, 20 preferablyinclude an optical waveguide such as an optical fiber 26 encased orembedded in a carrier 28 or larger diameter glass structure allowing thefiber 26 to be optically coupled to the glass plug 18. U.S. patentapplication Ser. No. 10/755,722, entitled “Low-Loss Large-DiameterPigtail” and hereby incorporated by reference in its entirety, describesexemplary pigtails that can facilitate subsequent optical connection ofthe fiber 26 to other fibers, connecters, or other optical components bysuitable splicing techniques known in the art. Further, U.S. applicationSer. No. 10/755,708, entitled “Large Diameter Optical Waveguide Splice,”which is herein incorporated by reference in its entirety, describes alarge-diameter splice suitable for splicing the fiber pigtails 19, 20 tothe glass plug 18. For some embodiments, the glass plug 18 can bespliced to or otherwise optically coupled with fibers in opticalcommunication with each end of the glass plug 18 by other techniques andmethods.

Sealing of the optical waveguide element 14 with respect to the fronthousing 10 occurs at and/or around the glass plug 18 to enable isolationof fluid pressure in communication with a first end 22 of the passageway16 from fluid pressure in communication with a second end 24 of thepassageway 16. This sealing of the glass plug 18 with respect to thefront housing 10 provides the feedthrough capabilities of thefeedthrough assembly 100. In the embodiment shown in FIG. 1, the glassplug 18 has a cone shaped tapered surface 50 for seating against acomplimentary tapered seat 51 of the front housing 10. Engagementbetween the tapered surface 50 and the complimentary tapered seat 51that is located along the passageway 16 forms a seal that seals offfluid communication through the passageway 16. The glass plug 18 can bemachined to provide the cone shaped tapered surface 50. Additionally,the glass plug 18 is preferably biased against the tapered seat 51 usinga mechanical preload.

A recess 30 formed in one end of the front housing 10 aligns with acorresponding recess 31 in one end of the back housing 12 where thehousings 10, 12 are coupled together. Preferably, the front housing 10is welded to the back housing 12 along mated features thereof. Thehousings 10, 12 preferably enclose the glass plug 18, a biasing membersuch as a first stack of Belleville washers 34, and a plunger 32, whichare all disposed within the recesses 30, 31.

The first stack of Belleville washers 34 supply the mechanical preloadby pressing the plunger 32 onto an opposite end of the glass plug 18from the tapered surface 50. Since the plunger 32 is moveable with theglass plug 18, this pressing of the plunger 32 develops a force to biasthe glass plug 18 onto the tapered seat 51 of the front housing 10located along the passageway 16 that passes through the front housing10. Transfer of force from the plunger 32 to the glass plug 18 can occurdirectly via an interface 54 between the two, which can include matingconical surfaces. The first stack of Belleville washers 34 compressbetween a base shoulder 44 of the recess 31 in the back housing 12 andan outward shoulder 46 of the plunger 32 upon make-up of the fronthousing 10 to the back housing 12. Once the back housing 12 is welded orotherwise attached to the front housing 10 in order to keep the frontand back housings 10, 12 connected, the first stack of Bellevillewashers 34 maintains the compression that supplies force acting againstthe plunger 32.

In some embodiments, the feed through assembly 100 further includes agasket member 52 disposed between the tapered seat 51 and the taperedsurface 50 of the glass plug 18. As shown in FIG. 1, the gasket member52 comprises an annular gasket. The gasket member 52 may be a gold foilthat is shaped to complement the tapered surface 50 and the tapered seat51. The gasket member 52 deforms sufficiently to accommodateimperfections on the tapered surface 50 and/or the tapered seat 51,thereby completing the seal and reducing stress between contactingsurfaces due to any imperfections on the surfaces. Gold is preferredbecause of its ability to withstand high temperature, its ductility andits inert, non-reactive, non-corrosive nature. However, other materialspossessing these characteristics may also be suitable, includingaluminum, lead, indium, polyetheretherketone (“PEEK™”), polyimide, othersuitable polymers, and combinations thereof.

An additional gasket member (not shown) may be disposed between theinterface 54 of the glass plug 18 and the plunger 32 for someembodiments to reduce the surface stress that may occur between thesetwo components. In further embodiments, a layer of gold or othersuitable material is deposited on the contact surfaces as an alternativeto using the gasket member 52. For example, the gold may be depositedusing chemical vapor deposition, physical vapor deposition, plating, orcombinations thereof to reduce surface stress and maximize the sealperformance. Other embodiments utilize the gasket member 52 punched fromsheets of a gasket material.

For some embodiments, the housings 10, 12 additionally enclose acup-shaped backstop sleeve 36, a second stack of Belleville washers 38,a perforated washer 40, and a centering element 42 that are all disposedwithin the recesses 30, 31. An outward shoulder 56 of the backstopsleeve 36 is trapped by the end of the front housing 10 and an inwardshoulder 57 along the recess 31 in the back housing 12. Contact uponsandwiching of the shoulder 56 of the backstop sleeve 36 provides thepoint at which the housings 10, 12 are fully mated and can be securedtogether. Clearance is provided such that the end of the back housing 12does not bottom out prior to the housings 10, 12 being fully mated.

The centering element 42 includes an elastomeric sealing componentdisposed between the glass plug 18 and the front housing 10 that can actas a back-up seal in addition to facilitating alignment of the glassplug 18 with respect to the seat 51. Although the centering element 42is described as providing a back up seal to the tapered surface 50 ofthe glass plug 18 seated with the gasket member 52 on the complimentarytapered seat 51, the centering element 42 can be omitted or usedindependently to seal off the passageway 16 through the housings 10, 12in other embodiments.

In some applications, the pressure in the recesses 30, 31 entering fromthe second end 24 of the passageway 16 is higher than the pressureentering from the first end 22 of the passageway 16. This pressuredifferential advantageously causes the centering element 42 to deformand press against the wall of the recess 30 and the wall of the glassplug 18, thereby creating a pressure energized seal. In someembodiments, one or more holes or annular channels 43 are formed on theouter surface of the high pressure side of the centering element 42.These holes or channels 43 facilitate the deformation of the centeringelement 42 and the formation of the seal between the centering element42 and the walls of the recess 30 and the glass plug 18. Additionally,the perforated washer 40 enables pressurized fluid to fill the centeringelement 42 for providing the energized seal.

Preferably, force transferred through the perforated washer 40 biasesthe centering element 42 into the recess 30. The second stack ofBelleville washers 38 pressed by the backstop sleeve 36 supplies thepreloading force to the perforated washer 40. The second stack ofBelleville washers 38 allow a maximum pressure force to act on thecentering element 42 such that pressure of the centering element 42against the wall of the glass plug 18 does not override force being puton the glass plug 18 to press the tapered surface 50 against the seat51.

Embodiments of the feedthrough assembly 100 are capable of performing intemperature environments of between −50° C. and 300° C. Additionally,the feedthrough assembly 100 is capable of withstanding pressure up toabout 30 kpsi.

Embedding Diagnostic Sensors

FIG. 2 illustrates a cross section view of an optical waveguidefeedthrough assembly 200 that operates similar to the feedthroughassembly 100 shown in FIG. 1. However, the feedthrough assembly 200includes first and second diagnostic sensors 201, 202 disposed within aglass plug 218. The diagnostic sensors 201, 202 can include any opticalsensing element, such as fiber Bragg gratings, capable of reflecting ortransmitting an optical signal in response to a parameter beingmeasured. The first diagnostic sensor 201 is disposed within the glassplug 218 proximate an interface 254 where a plunger 232 pushes on theglass plug 218. The second diagnostic sensor 202 is disposed within theglass plug 218 proximate where a tapered surface 250 of the glass plug218 mates with a seat 251. Preferably, each of the diagnostic sensors201, 202 span a length of the glass plug 218 across the respectivefeature that the sensor is proximate.

Interpreting the signals generated by the sensors 201, 202, such as byuse of a suitable algorithm or comparison to a calibration, enablesmonitoring of temperature and/or pressure. This detection ability allowsreal-time monitoring of the state of the feedthrough assembly 200.Information derived from the sensors 201, 202 can be beneficial bothduring fabrication of the feedthrough assembly 200 and during usethereof. For diagnostic purposes, signals received from the secondsensor 202 can be monitored to identify when and/or if proper contact ofthe tapered surface 250 with the seat 251 occurs to ensure that sealingis established or maintained. Further, monitoring one or both thesensors 201, 202 can ensure that excess force that might break the glassplug 18 is not applied to the glass plug 18 in embodiments where theamount of force can be controlled. Monitoring signals received from thefirst sensor 201 can detect the presence and condition of hydrostaticloads from surrounding fluid since these hydrostatic loads dominate theresponse of the first sensor 201. When the feedthrough assembly 200 ispart of a wellhead outlet of an oil/gas well, the sensors 201, 202 canbe used to detect pressure increases and set an alarm indicating thatseals have been breached in the well.

FIGS. 3-5 illustrate graphs of signals received from the diagnosticsensors 201, 202 where the feedthrough assembly 200 is at a fixedtemperature but has different pressures introduced at end 224 for eachgraph. In all of the graphs herein, first sensor responses 301correspond to signals received from the first sensor 201 while secondsensor responses 302 correspond to signals received from the secondsensor 202. In FIG. 3, an initial distortion or spreading of the secondsensor response 302 visible specifically as a spectral chirp 303,providing positive feedback that preload of the glass plug 18 at thetapered surface 250 against the seat 251 has been established.

As visible in FIGS. 4 and 5, this distortion in the second sensorresponses 302 grows relative to pressure due to non-uniform seal loads.However, the first sensor responses 301 show little change as pressureincreases since uniform hydrostatic pressure dominates the first sensor201. Additionally, the first sensor responses 301 provide an indicationof a thermo-mechanical state of the housing of the feedthrough assembly200 and a small pressure driven change in the preload of the plug 232.

FIGS. 6-8 show graphs of signals received from the diagnostic sensors201, 202 where the feedthrough assembly 200 is at a fixed pressure butis at a different temperature for each graph. The graphs show that astemperature increases both of the responses 301, 302 shift in wavelengthrelative to the temperature increase in the same direction. For example,the peak at approximately 1534.5 nanometers (nm) in the first responses301 at 25° C. shifts to approximately 1536.5 nm at 194° C. Other thansmall changes from temperature driven changes in the preloads, shapes ofthe responses 301, 302 do not change with temperature changes.

With reference to FIG. 1, pressure entering the first end 22 of thepassageway 16 may be significantly higher than the pressure entering thesecond end 24 of the passageway 16 in some applications. In thisinstance, if the higher pressure from the first end 22 exceeds athreshold value, then the seals formed by the seated tapered surface 50of the glass plug 18 and/or the centering element 42 may be unseated.Accordingly, non-epoxy feedthrough assemblies in some embodiments can beadapted to seal against pressure from either side of a glass plug.

A Bi-Directional Seal Assembley

FIG. 9 shows an exemplary feedthrough assembly 900 having abi-directional pressurized seal assembly 930. A cone shaped glass plug920 is disposed in a recess 925 of a feedthrough housing 910 formed bytwo body sections 911, 912. The body sections 911, 912 can be coupledtogether using a weld or various other coupling configurations. A bore915 sized to accommodate portions of an optical waveguide element 922 oneither side of the glass plug 920 extends through the feedthroughhousing 910. A tapered seat 913 can be formed on each body section 911,912 for receiving the glass plug 920. Similar to the embodiment shown inFIG. 1, a gasket member 945 such as an annular gold foil can be disposedbetween the glass plug 920 and the tapered seats 913 of the bodysections 911, 912. The symmetrical configuration of tapered seats 913 insections 911, 912 creates the primary bidirectional seal design.

In one embodiment, a back-up bi-directional seal assembly 930 isdisposed in the recess 925 to provide an additional seal against anyleakage from either body section 911, 912. The seal assembly 930includes two cup-shaped, annular sealing elements 931, 932 and apositioning device 940 to maintain the sealing elements 931, 932 intheir respective seal seats 941, 942. The sealing elements 931, 932 arepositioned such that their interior portions are opposed to each otherand the positioning device 940 may be disposed in the interior portionsof the sealing elements 931, 932. The positioning device 940 maycomprise a preloaded spring to bias the sealing elements 931, 932against their respective seal seats 941, 942, or against the bodysections 911, 912. In one embodiment, the sealing elements 931, 932 aremade of an elastomeric material. The sealing elements 931, 932 can alsocomprise other suitable flexible materials capable of withstanding hightemperature and high pressure.

In operation, if fluid leaks through the tapered surfaces between theglass plug 920 and the first body section 911, then the fluid pressureforces the glass plug 920 against the tapered seat in the body section912 to activate the reverse direction seal. The fluid pressure will alsoact against the second sealing element 932, which is biased against thesecond body section 912. Particularly, the fluid pressure acts on theinterior portion of the second sealing element 932 and urges sealinglips 934 of the second sealing element 932 outward, thereby sealing offany fluid path between the second sealing element 932 and the glass plug920 and between the second sealing element 932 and the body section 911.In this manner, the leaked fluid is prevented from entering the bore ofthe second body section 912 because of redundant seals.

Similarly, if fluid leaks through the tapered surfaces between the glassplug 920 and the second body section 912, then the fluid pressure forcesthe glass plug 920 against the tapered seat 913 in body section 911. Thefluid pressure will also act against the first sealing element 931biased against the first body section 911. In this respect, the fluidpressure causes sealing lips 933 of the first sealing element 931 tosealingly engage the glass plug 920 and the body section 911. Thus, theleaked fluid is prevented from entering the of bore of the first bodysection 911 because of redundant seals.

Feedthrough Assembly with Compression Bushing

FIG. 10 illustrates a cross sectional view of an optical waveguidefeedthrough assembly 500 that includes a housing 110, an externallythreaded bushing 102, a compression driver bushing 104, a compressionseal element 106, and a glass plug 118 portion of an optical waveguideelement that sealingly passes through the housing 110. The bushings 102,104 and the seal element 106 are disposed adjacent to one another in arecess 130 in the housing 110 and encircle a portion of the glass plug118. Specifically, the externally threaded bushing 102 threads into aportion of the recess 130 in the housing 110 defining mating internalthreads. The seal element 106 is located next to the driver bushing 104and proximate an inward tapering cone 131 along the recess 130 in thehousing 110.

A seal can be established with the glass plug 118 with respect to thehousing 110 by driving the seal element 106 down the cone 131. Toestablish this seal, rotation of the threaded bushing 102 with respectto the housing 110 displaces the threaded bushing 102 further into therecess 130 due to the threaded engagement between the threaded bushing102 and the housing 110. The driver bushing 104 in turn moves furtherinto the recess and pushes the sealing element 106 toward the cone 131.One function of the driver bushing 104 includes reducing torquetransferred to the seal element 106 from the threaded bushing 102.

Preferably, the glass plug 118 has a cone shaped tapered surface 150 forseating against a complimentary tapered seat 151 of the housing 110. Theengagement between the tapered surface 150 and the complimentary taperedseat 151 can also or alternatively seal off fluid communication throughthe housing 110 around the glass plug 118 in a redundant manner. Agasket member 152 such as an annular gold foil can be disposed betweenthe tapered surface 150 of the glass plug 118 and the tapered seat 151of the housing 110 to reduce stress risers.

FIG. 11 illustrates the optical waveguide feedthrough assembly 500 aftercompressing the seal element 106. The seal element 106 packs within anannulus between an exterior of the glass plug 118 and an interior of thehousing 110 after being driven down the cone 131. Once packed in theannulus, the seal element 106 provides sealing contact against both theglass plug 118 and the housing 110. Examples of suitable materials forthe seal element 106 include TEFLON™, VESPEL™, polyimide, PEEK™, ARLON™,gold or other ductile metals for high temperature applications. Duringlower temperature usage, element 106 can be nylon, DELRIN™ or metal suchas tin or lead. The driving of the seal element 106 can additionallymove the glass plug 118 to force the tapered surface 150 to mate withthe seat 151. The glass plug 118 is of sufficient diameter andstructural integrity that the compression of the seal element 106 aroundthe glass plug does not disturb the optical qualities thereof. Thefeedthrough assembly 500 is capable of sealing the glass plug 118 withrespect to the housing 110 regardless of which side of the housing 110is exposed to a higher pressure.

An Additional Exemplary Feedthrough Assembly

FIG. 12 shows a cross-section view of a feedthrough assembly 400 thatincludes a feedthrough housing 410 for retaining a glass plug 418. Arecess 425 is formed in one end of the housing 410 to receive the glassplug 418. Preferably, the recess 425 has a corresponding tapered seat451 for receiving a cone shaped tapered surface 450 of the glass plug418. The glass plug 418 is preferably biased against the tapered seat451 that is located along a bore 416 that connects to the recess 425 andprovides a passageway through the housing 410.

In one embodiment, a fitting 436 having an axial bore 437 extendingtherethrough is disposed between the glass plug 418 and a washer cap412. One end of the fitting 436 has a surface that mates with the glassplug 418 and an outer diameter that is about the same size as the innerdiameter of the recess 425. In this respect, the fitting 436 assistswith supporting the glass plug 418 in the recess 425. The other end ofthe fitting 436 has a neck 435 that connects to the washer cap 412.Particularly, a portion of the neck 435 fits in a hole of the washer cap412. The washer cap 412 may be attached to the feedthrough housing 410by any manner known to a person of ordinary skill in the art, such asone or more screws or bolts. For example, bolts 438 (two of three arevisible in FIG. 12) may be used to attach the washer cap 412 to thefeedthrough housing 410 via three screw holes 440 (only one is visiblein FIG. 12) formed through the washer cap 412 and into the feedthroughhousing 410.

The inner portion of the washer cap 412 facing the feedthrough housing410 has a cavity 431 for retaining a preload member such as a spring. Inone example, the preload member is a Belleville washer stack 434. Thewasher stack 434 may be disposed on the neck 435 of the fitting 436 andbetween the washer cap 412 and an outward shoulder 446 formed by areduced diameter of the neck 435 of the fitting 436. In this manner, thewasher stack 434 may exert a preloading force on the glass plug 418 tomaintain a seal between the glass plug 418 and the tapered seat 451 ofthe feedthrough housing 410. Similar to the embodiments described above,a gasket member such as an annular gold foil (not shown) can be disposedbetween the glass plug 418 and the tapered seats 451 and/or the glassplug 418 and the fitting 436.

The feedthrough assembly 400 may further include a centering element 442to act as a back-up seal. The centering element 442 comprises anelastomeric sealing component that is disposed between the glass plug418 and the feedthrough housing 410. A pressure differential across theglass plug 418 advantageously causes the centering element 442 to deformand press against the wall of the recess 425 and the wall of the glassplug 418, thereby creating a pressure energized seal. Although thecentering element 442 is described as providing a back up seal, thecentering element 442 may be used independently to seal off the bore 416of the feedthrough housing 410.

The invention heretofore can be used and has specific utility inapplications within the oil and gas industry. Further, it is within thescope of the invention that other commercial embodiments/uses exist withone such universal sealing arrangement shown in the figures andadaptable for use in (by way of example and not limitation) industrial,chemical, energy, nuclear, structural, etc. While the foregoing isdirected to preferred embodiments of the invention, other and furtherembodiments of the invention may be devised without departing from thebasic scope thereof, and the scope thereof is determined by the claimsthat follow.

What is claimed is:
 1. An optical waveguide feedthrough assembly,comprising: a housing having a bore therethrough with an inward taperingconical surface located along a length of the bore; an optical waveguideelement having a plug portion in optical communication with two opticalwaveguide portions extending from each end of the plug portion; acompression seal element disposed around the plug portion within thebore proximate the conical surface; and an externally threaded bushingmated with an internal threaded portion of the bore of the housing,wherein the bushing is rotatable with respect to the housing to drivethe seal element down the conical surface and pack an annulus betweenthe housing and the plug portion.
 2. The assembly of claim 1, furthercomprising a compression driver bushing disposed between the sealelement and the threaded bushing.
 3. The assembly of claim 1, whereinthe plug portion comprises a tapered surface for mating with acomplimentary tapered seat disposed in the housing located along alength of the bore.
 4. The assembly of claim 3, further comprising anannular gasket member disposed between the complementary tapered seatand the tapered surface of the plug portion.
 5. The assembly of claim 3,further comprising a gold film disposed between the complementarytapered seat and the tapered surface of the plug portion.
 6. An opticalwaveguide feedthrough assembly, comprising: a housing having a face anda bore extending therethrough; and an optical waveguide element having asealing surface for mating with the face without epoxy, wherein theoptical waveguide element has a core and cladding.
 7. The assembly ofclaim 6, wherein the face comprises a concave frustoconical section andwherein the sealing surface comprises a complimentary convexfrustoconical section.
 8. The assembly of claim 7, wherein the housingincludes an opposing concave frustoconical section that is spaced fromand oriented opposite the concave frustoconical section, and thewaveguide element comprises a complementary opposing convexfrustoconical section for mating with the opposing concave frustoconicalsection.
 9. The assembly of claim 6, wherein the optical waveguideelement comprises a large diameter waveguide having a center plugportion and a pair of concentric tail sections extending therefrom. 10.The assembly of claim 6, further comprising an annular gasket memberdisposed between the sealing surface and the face.
 11. The assembly ofclaim 10, wherein the gasket member comprises a ductile material. 12.The assembly of claim 10, wherein the gasket member comprises a materialselected from the group consisting of gold, aluminum, lead, indium,polyetheretherketone, polyimide, and combinations thereof.
 13. Theassembly of claim 6, further comprising a biasing member for biasing thewaveguide element against the housing to force the sealing surface ofthe waveguide element to mate with the face of the housing.
 14. Theassembly of claim 6, further comprising a sealing element disposedbetween the housing and a surface of the waveguide element, wherein thesealing element is biased into position against the waveguide elementand the housing by a biasing member.
 15. The assembly of claim 6,further comprising a sealing element disposed between the housing and asurface of the waveguide, wherein the sealing element provides abi-directional seal.